Zero tolernace: A woman walks past an armoured vehicle as police officers take cover during the operation to clean up Rio's drug gang-ridden slums before the city hosts the World Cup in 2014 and the Olympics in 2016

Gangs members have responded to the offensive against strongholds where they have held sway for decades by setting up roadblocks on major routes to rob motorists, torching more than 40 cars and buses and shooting at police posts.

Authorities say that when police arrive, gang members flee into nearby shanty towns.

The officers arrived in Vila Cruzeiro yesterday under the cover of police helicopters and amid the rattle of gunfire despite the gang members' efforts to block access with burning vehicles.

As police entered, dozens of gangsters were seen fleeing down jungle-covered hills, across an area known as 'the green hell', to a neighbouring gang stronghold, the Alemao complex of shanty towns.

The state police would have additional help today from government law enforcement to hold on to Vila Cruzeiro, Rio state public safety director Jose Beltrame said.

Mr Beltrame said the police were in Vila Cruzeiro 'and we're not leaving'.

Diving for cover: Police said they arrested 11 men and seized gallons of petrol and sticks of dynamite

Fleeing: Drug gang members left the Vila Cruzeiro slum as police began to pour in

As part of the pre-World Cup and Olympic clean-up, authorities have established permanent police posts in 13 slums over the past two years to try to bring basic services to the communities and rid them of drug trafficking-related violence.

A member of the elite BOPE police unit who would only give his last name, Malta, said as he waited for his turn to go into Vila Cruzeiro: 'The idea is to go in and take control.

'We can't live like this with these people threatening our families. It's zero tolerance now.'

Crackdown: Heavily-armed police officers frisk several suspects during the operation